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1.
以氧化铁和无定型硼粉为原料,反应气氛为碳气氛,在1 400℃下利用化学气相沉积法(CVD)制备出氮化硼纳米管。X射线研究表明,对应着六方氮化硼晶面的特征衍射峰非常清晰。采用扫描电子显微镜(SEM)对样品的结构与形貌进行表征,结果表明,样品属于一端开口的竹节状BN纳米管。 相似文献
2.
The fracture behavior of multilayer Si3 N4 /BN ceramics in bending has been studied. The materials were prepared by a process of tape casting, coating, laminating, and hot pressing. The Si3 N4 layers were separated by thin, weak BN interlayers. Crack patterns in bending bars were examined with a scanning electron microscope. The weak layers deflected cracks in bending and thus prevented catastrophic failure. In one well-aligned multilayer ceramic A, a main crack propagated through the specimen although along a zigzag path. A second multilayer ceramic B was made to simulate a wood grain structure. Its failure was dominated by shear cracking along the weak BN layers. Besides crack deflection, interlock bridging between toothlike layers in the wake of the main crack appeared also to contribute to toughening. 相似文献
3.
A method to synthesize boron nitride coating on the surface of carbon nanotubes (nanofibers) without damaging the tube walls has been developed. A reaction between boric acid and ammonia was performed at moderate temperatures on the surface of carbon nanotubes to form boron nitride (BN) coatings. The surface structure of the carbon nanotubes significantly influences the morphology of the boron nitride coating. If the surface of the tubes is free of defects, highly crystallized insulating BN nanotubes can encapsulate carbon nanotubes. On the surface of carbon nanotubes with disordered wall structure, a polycrystalline BN sheath was produced. 相似文献
4.
Dmitri Golberg Yoshio Bando Yang Huang Zhi Xu Xianlong Wei Laure Bourgeois Ming-Sheng Wang Haibo Zeng Jing Lin Chunyi Zhi 《Israel journal of chemistry》2010,50(4):405-416
Herein the recent experiments performed by the authors on fabricated multi-walled BN nanotubes and monoatomic BN graphene-like nanosheets are reviewed. The results are presented in several sections, namely: (i) method for high-yield synthesis of thin, defect-free BN nanotubes of only a few-layers, with external diameters below 10 nm; (ii) verification of BN nanotube piezoelectrical behavior and its electrically-induced thermal decomposition under combined resistive heating and electrical charging in a transmission electron microscope; (iii) the first direct measurements of the true tensile strength and Young’s modulus of BN nanotubes, using newly developed nanotensile tests inside an electron microscope; the measured values were found to be ∼30 GPa and ∼900 GPa, respectively; and (iv) diverse kinetic processes taking place within the prepared monoatomic BN sheets (so-called “white graphenes”) affiliated with intensive knock-on B and N atom displacements under high energy electron beam irradiation in an aberration-corrected medium-voltage high-resolution transmission electron microscope. 相似文献
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Elevated-Temperature Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics 总被引:1,自引:0,他引:1
A unique, all-ceramic material capable of nonbrittle fracture via crack deflection and delamination has been mechanically characterized from 25° through 1400°C. This material, fibrous monoliths, was comprised of unidirectionally aligned 250 μm diameter silicon nitride cells surrounded by 10 to 20 μm thick boron nitride cell boundaries. The average flexure strengths of fibrous monoliths were 510 and 290 MPa for specimens tested at room temperature and 1300°C, respectively. Crack deflection in the BN cell boundaries was observed at all temperatures. Characteristic flexural responses were observed at temperatures between 25° and 1400°C. Changes in the flexural response at different temperatures were attributed to changes in the physical properties of either the silicon nitride cells or boron nitride cell boundary. 相似文献
7.
Desiderio Kovar M. D. Thouless § John W. Halloran 《Journal of the American Ceramic Society》1998,81(4):1004-1112
Crack deflection and the subsequent growth of delamination cracks can be a potent source of energy dissipation during the fracture of layered ceramics. In this study, multilayered ceramics that consist of silicon nitride (Si3 N4 ) layers separated by boron nitride/silicon nitride (BN/Si3 N4 ) interphases have been manufactured and tested. Flexural tests reveal that the crack path is dependent on the composition of the interphase between the Si3 N4 layers. Experimental measurements of interfacial fracture resistance and frictional sliding resistance show that both quantities increase as the Si3 N4 content in the interphase increases. However, contrary to existing theories, high energy-absorption capacity has not been realized in materials that exhibit crack deflection but also have moderately high interfacial fracture resistance. Significant energy absorption has been measured only in materials with very low interfacial fracture resistance values. A method of predicting the critical value of the interfacial fracture resistance necessary to ensure a high energy-absorption capacity is presented. 相似文献
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Satoshi Nakano Hiroyuki Ikawa Osamu Fukunaga 《Journal of the American Ceramic Society》1992,75(1):240-243
Cubic boron nitride ( c -BN) was synthesized by the decomposition of Mg3 BN3 under high pressure and high temperature. The minimum pressure for c -BN synthesis was 4 GPa, which was 1 GPa lower than that of the conventional catalytic process. The decomposition of Mg3 BN3 was observed only when H2 O was added. Therefore, the reaction was as follows: Mg3 BN3 + 3H2 O = 3MgO + c -BN + 2NH3 . The c -BN crystals obtained were tetrahedron in shape and about 10 μ m in diameter. 相似文献
10.
Fracture toughness behavior, stress–strain behavior, and flaw resistance of pressureless-sintered Si3 N4 -BN ceramics are investigated. The results are discussed with respect to the reported thermal shock behavior of these composites. Although the materials behave linear-elastic and exhibit no R -curve behavior, their flaw resistance is different from that of other linear-elastic materials. Whereas the critical thermal shock temperature difference (Δ T c ) is enhanced by adding BN, the content of BN has no influence on the strength loss during severe thermal shocks. 相似文献
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Nathan Jacobson Serene Farmer Arthur Moore Haluk Sayir 《Journal of the American Ceramic Society》1999,82(2):393-398
High-temperature oxidation of monolithic boron nitride (BN) is examined at 900–1200°C. Hot-pressed BN and both low- and high-density chemically vapor-deposited BN are studied. The oxidation product is B2 O3 ( l ) and the oxidation kinetics are sensitive to crystallographic orientation, porosity, and impurity levels. The B2 O3 product also reacts readily with ambient water vapor in the test furnace (ppm levels) to form the volatile species HBO2 ( g ), leading to overall paralinear kinetics. The linear rate constant extracted from these experiments agreed with that predicted from diffusion of HBO2 ( g ) across a static boundary layer. 相似文献
13.
Influence of Microstructure and Temperature on the Interfacial Fracture Energy of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics 总被引:1,自引:0,他引:1
The microstructure and interfacial fracture energy of silicon nitride/boron nitride fibrous monoliths, GammaBN , were determined as a function of starting silicon nitride composition and temperature using the method described by Charalambides. The glassy phase created by the sintering aids added to the silicon nitride cells was shown to migrate into the boron nitride cell boundaries during hot-pressing. The amount of glassy phase in the boron nitride cell boundaries was shown to strongly influence GammaBN at room temperature, increasing the fracture energy with increasing amounts of glass. Similar trends in the interfacial fracture energy as a function of temperature were demonstrated by both compositions of fibrous monoliths, with a large peak in GammaBN observed over a narrow temperature range. For silicon nitride cells densified with 6 wt% yttria and 2 wt% alumina, the room-temperature interfacial fracture energy was 37 J/m2 , remaining constant through 950°C. A sharp increase in GammaBN , to 60 J/m2 , was observed between 1000° and 1050°C. This increase was attributed to interactions of the crack tip with the glassy phase in the boron nitride cell boundary. Measurements at 1075°C indicated a marked decrease in GammaBN to 39 J/m2 . The interfacial fracture energy decreased with increasing temperature in the 1200° to 1300°C regime, plateauing between 17 to 20 J/m2 . A crack propagation model based on linkup of existing microcracks and peeling/cleaving boron nitride has been proposed. 相似文献
14.
Si3 N4 test bars containing additions of BN, B4 C, and C, were hot isostatically pressed in Ta cladding at 1900° and 2050°C to 98.9% to 99.5% theoretical density. Room-temperature strength data on specimens containing 2 wt% BN and 0.5 wt% C were comparable to data obtained for Si3 N4 sintered with Y2 O3 , Y2 O3 and Al2 O3 , or ZrO2 . The 1370°C strengths were less than those obtained for additions of Y2 O3 or ZrO2 but greater than those obtained from a combination of Y2 O3 and Al2 O3 . Scanning electron microscope fractography indicated that, as with other types of Si3 N4 , roomtemperature strength was controlled by processing flaws. The decrease in strength at 1370°C was typical of Si3 N4 having an amorphous grainboundary phase. The primary advantage of non-oxide additions appears to be in facilitating specimen removal from the Ta cladding. 相似文献
15.
John A. Hanigofsky Karren L. More W. J. Lackey Woo Y. Lee Garth B. Freeman 《Journal of the American Ceramic Society》1991,74(2):301-305
The composition and microstructure of dispersed-phase ceramic composites containing BN and AIN as well as BN and AIN single-phase ceramics prepared by chemical vapor deposition have been characterized using X-ray diffraction, scanning electron microscopy, electron microprobe, and transmission electron microscopy techniques. Under certain processing conditions, the codeposited coating microstructure consists of small single-crystal AIN fibers (whiskers) surrounded by a turbostratic BN matrix. Other processing conditions resulted in single-phase films of AIN with a fibrous structure. The compositions of the codeposits range from 2 to 50 mol% BN, 50 to 80 mol% AIN with 7% to 25% oxygen impurity as determined by electron microprobe analysis. 相似文献
16.
Bo Zhong Zhenfei Chai Long Xia Guangwu Wen Shuaifeng Cheng Yudong Huang 《International Journal of Applied Ceramic Technology》2016,13(5):929-936
A new polymeric boron nitride (BN) precursor poly[(phenylamino)borazine] (PPAB) with good melt‐processing performance was successfully synthesized by reaction of B‐trichloroborazine (TCB), aniline, and N‐methylaniline under mild conditions. The as‐synthesized PPAB as well as its structural evolution during the ceramic conversion was studied by means of various complementary techniques. The effect of process parameters including monomer ratio, reaction time, and reaction temperature on the properties of polymers was investigated, and the optimized parameters were obtained. Gel permeation chromatography (GPC) analysis of typical PPAB revealed that the number‐average molecular weight (Mn) was 30,520 Da and the polymerization degree was 319. The polymer could be converted to BN ceramics under ammonia atmosphere at 1200°C with carbon content as low as 0.9wt%. The PPAB polymer could be melt‐spun into continuous polymer fibers by hand drawing, which could be further transformed into BN ceramic fibers with good quality. The PPAB polymer is promising for applications that require BN precursor with stable melt processability. 相似文献
17.
Preparation and Use of a Boron Nitride Precursor as Binder for the Densification of Boron Nitride 总被引:1,自引:0,他引:1
A precursor of boron nitride was prepared through the partial condensation of 2,4,6-trichloroborazine and bis-(trimethylsilyl)acetylene. This reaction was conducted at 100°C and is catalyzed by AlCl3 . The condensation product pyrolyzed at 800°C, producing trimethylsilyl chloride as a volatile product and a boron nitride rich residue containing 54 wt% of the initial weight. Mixtures of the precursor and commercial boron nitride were made and hot-pressed at 800°C and 27.6 MPa. A maximum density of 1.84 g/cm3 is reached at a loading corresponding to the deposition of 13 wt% residue derived from the precursor. Examination by analytical electron microscopy, including X-ray energy dispersive spectroscopy and electron energy loss spectroscopy analyses, revealed the location of material derived from the precursor in BN-binder composites through the presence of residual aluminum, silicon, and carbon. Crystallization of boron nitride from the precursor appears to have taken place, as deduced from the morphology of the phases observed and association with residual elements present in the binder. 相似文献
18.
Nathan S. Jacobson Gregory N. Morscher Darren R. Bryant Richard E. Tressler 《Journal of the American Ceramic Society》1999,82(6):1473-1482
The oxidation of BN composite interphases was examined with a series of model materials. Oxidation was examined in both low-water-vapor (∼20 ppm H2 O/O2 ) environments at 900°C and high-water-vapor (1% and 10% H2 O/O2 ) environments at 700° and 800°C. The low-water-vapor case was explored with layered BN/SiC materials. This case was dominated by borosilicate glass formation, and the 20 ppm water vapor gradually removed the boron from the glass, leaving a larger amount of SiO2 than would be expected from simple SiC oxidation. Layered SiC/BN/SiC materials were also used to study low-water-vapor oxidation effects within the composite. The high-water-vapor case was explored with SiC/BN/SiC minicomposites, and it was dominated by volatilization of BN as HBO2 ( g ), H3 BO3 ( g ), and H3 B3 O6 ( g ). A model for recession of the BN fiber coating was developed based on the gas-phase diffusion of these species out of the annular region around the SiC fiber and concurrent sealing of this annular region by oxidation. 相似文献
19.
Machinability of Silicon Nitride/Boron Nitride Nanocomposites 总被引:4,自引:0,他引:4
Takafumi Kusunose Tohru Sekino Yong-Ho Choa Koichi Niihara 《Journal of the American Ceramic Society》2002,85(11):2689-2695
The machinability and deformation mechanism of Si3 N4 /BN nanocomposites were investigated in the present work. The fracture strength of Si3 N4 /BN microcomposites remarkably decreased with increased hexagonal graphitic boron nitride ( h -BN) content, although machinability was somewhat improved. However, the nanocomposites fabricated using the chemical method simultaneously had high fracture strength and good machinability. Hertzian contact tests were performed to clarify the deformation behavior by mechanical shock. As a result of this test, the damage of the monolithic Si3 N4 and Si3 N4 /BN microcomposites indicated a classical Hertzian cone fracture and many large cracks, whereas the damage observed in the nanocomposites appeared to be quasi-plastic deformation. 相似文献
20.
Tadao Sato Toshihiko Ishii Nobuo Setaka 《Journal of the American Ceramic Society》1982,65(10):c162-c162
When rhombohedral BN, which has a layer structure with a three-layered stacking sequence, was shock-compressed at 40, 60, and 100 GPa, it was converted to cubic BN. Hexagonal BN was converted to wurtzite-type BN under the same conditions. These results indicate that the transformation proceeds by a diffusionless mechanism in which the stacking sequence of the BN layers in the starting materials is retained during the process. 相似文献